The art of photocomposing probably originated almost as early as the art of photography. In the late 1800's photographic output for a telegraph system was devised. Instead of hitting mechanical keys to print a message, the system used a photographic exposure of the letters to be printed. Since that time, serial printing of characters and other information by photography developed relatively slowly until the time was reached when science and engineering was ready for it. In the 1930's high intensity flash sources were developed so that all of a sudden it became possible to make a photographic exposure of a moving object and stop its motion in flight. At roughly the same time, logic circuitry began to develop to the point where it was possible to make a rapid selection of one of a number of objects and to select such objects at a precise time and position. Accordingly, in the mid 1940's, several people, virtually simultaneously, developed photocomposing machines which operated with moving images of alphanumeric characters, selecting these characters at relatively high speed and stopping the motion with a strobe flash. In relatively quick succession, at least three different photocomposing machines of this sort came into being as evidenced by Tansel, U.S. Pat. No. 2,725,803, Higonnet and Moyroud, U.S. Pat. 2,790,362, and Perry U.S. Pat. No. 2,876,687. Machines of the sort related to these patents have been developed during the years and have found an increasing place in the market. The art of photocomposing is steadily growing as a significant new way of generating a printing master.
Most recently with improvements in computers and automation, it is becoming possible to compose type by means of photocomposition at increasing speeds and with increasing quality of result. It is now possible to compose type either from a keyboard or coded signal input, which may be derived from punched tape or magnetic tape or from a source such as a transmission wire, and to compose the type with final printing quality such that it is almost indistinguishable from letter press printing and in many instances better than letter press.
One type of phototypesetting apparatus presently in commercial use includes a character storage drum as shown in Tidd, U.S. Pat. No. 3,721,174 which carries on a film strip a plurality of character fonts arranged in tandem around the periphery of the drum. The drum is rotated rapidly to bring the characters in sequence before an optical imaging system illuminated by a quickly pulsed light source. A particular character is selected by causing the light source to be pulsed when that character is registered with the imaging system. The end product of such phototypesetting apparatus is a photographic printing plate.
In the practice of phototypesetting, as with all typesetting, a large number of type fonts are made available for selective use according to the specifications of particular jobs. It is desirable that phototypesetting machines have the capability of selecting a character from the greatest possible number of fonts with the least expenditure of time and labor.
Many drum-type phototypesetting machines have the capability of storing a number of fonts in tandem around the periphery of the character storage drum; however, in general such machines require that the font combinations be preassembled and placed on a master film strip which is then secured on the periphery of the drum. In one commercially available machine, font interchangeability is provided by use of film strips carrying individual character fonts which are attached separately to the periphery of a drum and aligned by means of registration pins.
However, the described arrangement for providing individual font replacement or interchange has certain deficiencies. First, the accuracy with which the character fonts can be positioned and held on the drum, initially and especially after a period of use, is not acceptable. Secondly, the described arangement for providing selective replacement of individual character fonts is unnecessarily time consuming and laborious. Thirdly, it has been found that because of the dimensional flexibility of a film strip it is apt to bow, warp, or be otherwise distorted at high rotational speeds. This is particularly serious when the effect is to distort the registration between the characters and associated timing marks which customarily accompany the characters on a font strip. The problem of accurate location of the characters on the drum is particularly acute in machines having the capability of magnifying characters.
In Tidd, U.S. Pat. No. 3,721,174, discrete character carriers, each carrying a font of characters dispersed on a cylinder of revolution when the photocomposing machine is in operation, is disclosed as a high accuracy character storage and presentment device. The problem arising with this device is that it still can accommodate only a limited selection of characters and character fonts, somewhat fewer than are desired in todays highspeed machines.
In order to increase flexibility of the photocomposing machine a greater amount of characters and character fonts are required. A solution to increase the number of characters stored for certain foreign language applications was achieved in Ebner, U.S. Pat. No. 3,893,132. In this system, mirrors were used as the track selector device to position the appropriate character from a particular row of characters. A plurality of these mirrors each inclined at a slightly different position with respect to its rotatable platform so that each mirror when moved into position receives a selected flash from a single row of characters.
In another commercially available machine discs containing a plurality of font rows are attached to a mounting member which is perpendicularly attached to a movable arm. Consequently, the entire disc and support members are caused to move so that the machines optical path is approximately perpendicular to the surface of the entire disc.